In the field of laboratory tests, the analysis of blood components in samples is very important when various diseases of circulatory organs or the like of subjects are diagnosed. Depending to the type of diseases, the number of particular blood cells may increase or decrease, or the blood cells which normally do not exist therein appear in the peripheral blood, in some cases.
Recently, various automatic blood cell counters are commercialized in which the principles of flow cytometry are applied. By using such automatic blood cell counters, blood cells in samples can be automatically classified and counted.
Normally, leukocytes can be classified into five species, lymphocytes, monocytes, neutrophils, eosinophils and basophils. Among them, the number of basophils contained in blood samples is small. Therefore, the accuracy of the classification can be improved by measuring basophils in blood samples with the treatment exclusive for basophil measurements, compared to the measurement of basophils with the method in which leukocytes are classified into five species and basophils are measured in one measurement. Basophils have the specific characteristic such that they are less damaged compared to other types of leukocytes under an acidic condition. By utilizing such characteristics, discrimination of basophils from other types of leukocytes with the treatment exclusive for basophils is disclosed in Japanese Unexamined Patent Publication No. SHO 61 (1986)-88896 (Patent Document 1) and Japanese Unexamined Patent Publication No. HEI 7 (1995)-294518 (Patent Document 2).
An emergence of nucleated erythrocytes sometimes causes problems in a measurement of leukocytes. Nucleated erythrocytes have nuclei. In a measurement of leukocytes, even when erythrocytes are treated to be lysed, nuclei of nucleated erythrocytes remain to cause the signal similar to leukocytes, giving false positive error on the measurement of the number of leukocytes. In order to eliminate this effect and obtain the precise number of leukocytes, a blood sample is treated by the treatment exclusive for nucleated erythrocytes to measure the number of nucleated erythrocytes, the number of leukocytes in the same blood sample is measured by a different method, and then the number of nucleated erythrocytes is subtracted from the number of leukocytes obtained. Japanese Unexamined Patent Publication No. HEI 10 (1998)-339729 (Patent Document 3) discloses the discrimination of nucleated erythrocytes from leukocytes by applying the treatment exclusive for nucleated erythrocytes to blood samples.
However, the necessity of the treatments exclusive for respective blood cells as disclosed in the above Patent Documents 1 to 3 for the classification of basophils or nucleated erythrocytes requires a great deal of time and further makes measurement apparatus complicated or upsized. In addition, the usage of multiple reagents exclusive for respective blood cells comes expensive as overall cost for blood test. Accordingly, it is preferable that the treatments exclusive for blood cells are as less as possible.
Both basophils and nucleated erythrocytes can be measured by treating blood samples under an acidic condition. Therefore, there is a possibility that both basophils and nucleated erythrocytes can be measured in one measurement when a blood sample is treated under an acidic condition. Japanese Unexamined Patent Publication No. 2002-148261 (Patent Document 4) discloses that basophils and erythroblasts (nucleated erythrocytes) can be measured by mixing a sample with an aqueous solution containing a surfactant and an erythrocyte lysing agent which allows leukocytes and abnormal cells to be in the state suitable for staining, adding a staining agent containing a fluorescent dye to stain the cells and measuring the fluorescent intensity and the scattered light intensity with a flow cytometer.